Recently, display technologies using various methods such as a plasma display panel (PDP), a liquid crystal display (LCD) and the like that are used instead of a known braun tube in accordance with the development of optical technologies are suggested and sold. The higher properties of the polymer material for displays are required. For example, in the case of the liquid crystal display, according to the development toward the thin film, the lightness, and enlargement of the picture area, the wide viewing angle, the high contrast, the suppression of change in picture color tone according to the viewing angle and the uniformity of the picture display are particularly considered as important problems.
Therefore, various polymer films such as a polarizing film, a polarizer protection film, a retardation film, a plastic substrate, a light guide plate and the like are used, and as the liquid crystal, various modes of liquid crystal displays such as twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), in-plane switching (IPS) liquid crystal cells are developed. Since these liquid crystal cells have all intrinsic liquid crystal alignment, the intrinsic optical anisotropic property is ensured, and in order to compensate the optical anisotropic property, a film in which a retardation function is provided by stretching various kinds of polymers has been suggested.
In detail, since a liquid crystal display device uses high birefringence property and alignment of liquid crystal molecules, the birefringences are different according to the viewing angle and thus the color and brightness of the picture are changed. Thus, a retardation compensation according to the kind of liquid crystal molecule is required. For example, since most liquid crystal molecules that are used in a vertical alignment manner have the thickness refractive index that is larger than the average in-plane refractive index in a liquid crystal display surface, in order to compensate this, a compensation film in which the thickness refractive index is smaller than the average in-plane refractive index is required.
In addition, light does not pass through the front sides of two polarizing plates that are vertical to each other, but if the angle is inclined, the light axes of two polarizing plates are not vertical to each other, thus light leakage occurs. In order to compensate this, the compensate film that has the in-plane retardation is required. In addition, the display device using the liquid crystal requires both the thickness retardation compensation and the in-plane retardation compensation in order to widen the angle view.
Requirement of the retardation compensation film is to easily control the birefringence. However, the film birefringence is formed by a basic birefringence which belongs to the material and the alignment of polymer chains in the film. The alignment of the polymer chains is mostly forcibly performed by force applied from the outside or is caused by the intrinsic properties of the material, and the alignment-method of the molecules by the external force is to uniaxially or biaxially stretch the polymer film.
In the related art, there is a need to develop a polymer material that satisfies the above requirement properties in order to be used in displays.